Field of the Invention
Methods and systems for the decontamination of sulfur contaminants from hydrocarbons are provided. Specifically, methods and systems are provided for using methylmorpholine-N-oxide to remove sulfur contaminants from hydrocarbons in both surface and downhole applications.
Background of the Invention
Sulfur contaminants, for example hydrogen sulfide (H2S) can be produced by natural forces and as by-products of industrial processes. As a consequence of the offensive nature of, and potentially environmental and safety problems posed by sulfur containants, such as H2S, the release to the atmosphere of some sulfur contaminants may be regulated by environmental agencies.
Certain sulfur contaminants, particularly hydrogen sulfide and mercaptan compounds, are known to occur with fluid hydrocarbons in subterranean formations, such as coal beds and those that contain oil and/or gas. It is, thus, well known that sulfur contaminants may be dissolved or dispersed in fluid hydrocarbons recovered from such formations and/or separately produced with such hydrocarbons in the gas phase. Regardless of the form of occurrence, and particularly in the case of high concentrations thereof, it has long been important that sulfur contaminants be handled and treated using methods designed to prevent their release, for example, as a gas, to the environment. For purposes of this disclosure, “hydrocarbons” are defined to mean hydrocarbons which occur in the liquid phase, such as crude oil, and also hydrocarbons which occur in the gas phase, such as natural gas. Distinction between the matter phase of the hydrocarbons may be made with reference to a hydrocarbon fluid or a hydrocarbon gas. Still further, a hydrocarbon containing a sulfur contaminant, such as hydrogen sulfide and/or mercaptans, is referred to herein as being “sour.” For example, crude oil and natural gas recovered in a subterranean formation together with a sulfur contaminant may be referred to as “sour” crude and “sour” gas.
In addition to the natural occurrence of sulfur contaminants, such contaminants may also be produced in industrial operations and may result in contamination of refined hydrocarbon products, such as jet fuel, heating oil, petrochemical feedstocks and the like. Further, refineries and petrochemical plants are commonly contaminated with sulfur contaminants. These sulfur contaminants may typically be mitigated or removed as part of decontamination procedures, for instance, prior to vessel (e.g., large storage tanks) entry by individuals. A conventional approach to decontamination is to use hydrogen sulfide scavengers (e.g., liquid scavengers) such as triazine, acrolein, or formaldehyde. Such scavengers may rely on non-oxidative complexation and may be an economical approach for H2S decontamination. Liquid scavengers may tie up H2S as water-soluble compounds that may be discharged to wastewater treatment facilities. However, such scavengers have drawbacks. For instance, some of the reaction products may not be water-soluble, and some of the treatment chemicals may have associated toxicity or environmental restrictions in certain locations. In addition, some sulfur contaminants may only be removed by specific scavengers, for example, typically only acrolein may neutralize pyrophoric iron sulfides. Additionally, triazine treatments may raise the pH of effluent streams and as a result, may promote the formation of scales on metal surfaces. Formaldehyde reactions with H2S typically produce water insoluble products. Further, acrolein's benefits may be tempered by its toxicity.
Other methods have been developed and demonstrated to be effective at oxidizing and eliminating sulfur contaminants. Such methods include using permanganate (e.g., potassium permanganate), persulfate, sodium nitrite, ozone, hypochlorite, adducts of peroxide such as perborates and percarbonates, and long-chain amine oxides. The oxidizing chemicals may irreversibly convert sulfur contaminants (e.g., H2S) to harmless water soluble forms of sulfur, which may be compatible with effluent discharge. Each of these oxidizing compounds (i.e., oxidizing chemicals) have certain drawbacks. Hypochlorite may form dangerous chlorine compounds. Ozone and permanganate may require field mixing. Permanganate decontaminations may be further complicated by large amounts of reaction solids that are typically processed at additional cost. Percarbonates, as with permanganate, may also be exothermic in their reaction, which may be particularly dangerous since the hydrocarbons may combust. Further, if using treatments comprising strong oxidizers (i.e., permanganate, percarbonate, persulfate) with large exotherms, operations may typically be accomplished in small sequential batches outside the storage vessel in order to control the associated exotherm. As a result, these treatments may involve considerable time and therefore cost. Further, such action may render downhole treatment of hydrocarbons an impossibility. Additionally, the strong oxidizers may also be corrosive. Moreover, some of these compounds may also react violently with hydrocarbon components that may be present in sour sludge. For example, the strong oxidizers may be non-selective in their reaction and may react with many of the hydrocarbon components in which decontamination is desired.
Mild oxidizers such as amine oxides and nitrites may be effective at oxidizing sulfur contaminants to harmless forms of sulfur while having limited to no effect on hydrocarbons, unlike the strong oxidizers discussed above. Additionally, mild oxidizers may be added directly to a vessel or used downhole as their associated reactions may be non-exothermic. However, mild oxidizers also have drawbacks. For instance, typical long-chain amine oxides may pose foaming issues due to their surfactant nature. These amine oxides may also have limited efficiency for large amounts of H2S, since they are typically diluted in water to prevent gel formation. Further, some of the mild oxidizers may impart additional nitrogen to the hydrocarbons which may poison some downstream catalysts used during refining of the hydrocarbons. Nitrites may also have drawbacks, as their reaction with hydrogen sulfide produces ammonia. As a result, the nitrite oxidation reaction may be accompanied by a rise in pH, which at some point may cease the oxidation before it is complete.
Consequently, there is a need for improved methods and systems for decontaminating hydrocarbons contaminated with sulfur contaminants.